Servo synchronization with mechanical inter lock

ABSTRACT

A multi-range transmission for motor vehicles having a first gear and a second gear mounted side by side on a common shaft, and a synchronizing device, for matching the speed of the gears, located between the gears and movable axially relative thereto. An actuating element of the synchronizing device rotates with the first gear, the actuating element can be rotate with respect to the gearbox only through a limited angle of rotation and has a circumferential friction surface which can be brought into contact with an opposing friction surface of the second gear when axially moved. In order to permit synchronized shifting with a constant shift time, which is independent of the shift force applied manually, the actuator has a first inclined surface set at an angle to a radial plane which contacts a second inclined surface of with the first gear. In this way, when frictional engagement occurs, the actuating element is subject to an axial force which is directed toward the opposing friction surface of the second gear.

The invention concerns a multi-range transmission for motor vehicles,with a first gear and a second gear located next to one another on acommon shaft, with synchronizing devices located between the gears andmovable axially with respect to them for matching the speed of thegears, whereby one actuating element of the synchronizing devicesrotates with the first gear, however, rotable only within a limitedportion of the circumference, and with a circumferential frictionsurface which can be brought into contact with an opposing frictionsurface of the second gear when moved axially.

Transmissions of the type described are generally known as synchromeshtransmissions.

With customary transmissions of this type, the first gear rotates withthe shaft, the second gear rotates freely on the shaft. The second gearmeshes with a third gear which is located on and rotates with a secondshaft which is parallel to the first one. The synchronizing devices areusually synchronizing rings which rotate with the first gear and canrotate within a limited angle of rotation with respect to the gear. Ashift sleeve surrounding the external toothing of the gears can be madeto slide by a shift fork, whereby the shift sleeve has internal toothingwhich positively engages in the external toothing of the first andsecond gear, thus connecting the gears so they rotate together.

Before this unirotating connection can be made, however, the shiftsleeve slides the synchronizing ring--which usually has a conicalfriction surface--against the opposing surface of the second gear sothat, if there is a difference in rotational speed between the first andsecond gear, a friction moment is induced which rotates thesynchronizing ring by a stated finite angle of rotation with respect tothe first gear. In this rotated state, the synchronizing ring preventsfurther axial movement of the shift sleeve so the respective shift rangecannot be engaged until the first and second gears both rotate at thesame speed. Only after this is the case--the friction moment hastherefore reached zero--can the synchronizing ring rotate back to theinitial, unrotated, position (for example, as a result of the force of asuitable return spring), clearing the axial path for the shift sleeve sothe first and second gear can engage with each other, thus also engagingthe desired shift range.

From the above description explaining the operation of customarysynchromesh transmissions, it follows that the synchronizing procedureis highly dependent on how the vehicle drive executes the change ofshift range by operating the shift lever; if the shift sleeve is movedrelatively forcibly, thus thrusting the synchronizing ring with greatforce against the opposing surface of the second gear, a relativelylarge friction moment occurs immediately and the speed matching occursrelatively quickly. Conversely, the speed of the two gears is matchedrelatively slowly if the shift sleeve is moved with only a slight axialactuating force. This obviously influences the time required for therange change because the spreed gradient of the gear which is to beaccelerated or slowed depends on the amount of the friction moment anddirectly influences the shift time.

The wear on the friction surfaces of the synchronizing ring and theopposing surface as well as the wear on the toothing also naturallydepend on the force with which the shift sleeve is moved axially.

The objective of the invention is to further develop a transmission ofthe type described so that the synchronizing procedure takes placeindependently of the shift force applied by the driver.

This objective is implemented by the invention as follows: the actuatorhas a first surface which is slanted from the radial plane; it meetswith an opposing, second, inclined surface which rotates with the firstgear in such a manner that an axial force is applied by the actuatoragainst the opposing friction surface when friction occurs.

The invention completely fulfills this objective in the manner statedabove. When the driver wishes to shift the transmission range, he needonly initiate the synchronizing procedure by bringing the frictionsurfaces into contact with one another because the resulting frictionmoment immediately causes axial displacement of the actuator by means ofthe invention's wedge system; the axial displacement then increases thefriction moment in a specified manner. By adjusting the geometry of theinclined surfaces and the friction surfaces and selecting the frictioncoefficient, development of a friction moment within a pre-determinedtime frame results automatically, thus ensuring a synchronizingprocedure which always occurs uniformly.

This provides the additional advantage that a constant shift time can bespecified and wear can also be held constant, enabling the service lifeof the components to be precisely calculated. Lastly, the invention alsohas the advantage that it provides a considerable contribution towardautomatation of multi-range transmissions with spur-gear toothing andinterruption of tractive force because the self-regulation of thesynchronizing procedure as described above requires only to be triggeredfor initiation, which can be achieved easily with a simple mechanicaltransducer or similar initiator together with an electronic controlunit.

It has already been mentioned above that the invention is particularlysuitable for use in conventional multi-range transmissions characterizedby having a first gear which rotates with the shaft; that a second gearrotates on the same shaft, engaging an additional third gear whichrotates with a shaft located parallel to the first shaft; that the firstgear rotates with a synchronizing ring; that a first friction surface onthe synchronizing ring works together with an opposing friction surfaceon the second gear; that a sliding shift sleeve surrounds the first andsecond gear.

An advantage of these measures is that the invention can be integratedeasily into existing transmissions because only relatively minormodifications to the synchronizing ring and the gears and shift sleeveare necessary.

Based on the invention, the inclined surfaces can alternatively beeither on the first gear and on the synchronizing ring, or on the shiftsleeve and on the synchronizing ring, depending on which is morepractical with the space avabilable.

With a further design variant of the invention, the synchronizing ringsare located on both sides of the first gear and blocking devices areprovided to axially arrest one synchronizing ring when the othersynchronizing ring is moved.

Thus, the advantages of the invention are retained in the otherwisecustomary system of locating two synchronizing rings on either side of agear, with a shift sleeve which can be moved in both directions relativeto the gear. Because of the self-regulating synchronizing procedure withautomatically increasing friction moment, care must be taken to ensurethat none of the friction surfaces even momentarily, thus causingundesired synchronization in the transmission. The characteristicsmemtioned above eliminate the problem because the blocking devicesreliably prevent unintentional axial movement of the synchronizingrings.

One implemented form of this variant uses a ball obstructor as blockingdevice; a ball is located in an opening of the synchronizing ring,whereby the ball diameter is larger than the radial thickness of thesynchronizing ring in the area of the aperture; furthermore, the ballalso either engages only in a radial cavity of the first gear, or onlyin a radial cavity of the shift sleeve.

This is an advantage in that a blocking device is available which workswith low friction while ensuring the blocking function in everyoperating state.

Additional examples of versions of the invention are synchronizing ringsequipped with a resilient ring which the shift sleeve contacts in orderto engage the friction surface of one of the synchronizing rings withthe opposing surface.

This measure has the advantage that a pre-synchronization occurs becausecontact of the shift sleeve with the resilient ring increases thefriction moment between the two components beyond that provided by theslight, limited angle of rotation already mentioned.

In conclusion, there is another version of the invention in which theshift sleeve and the synchronizing ring are each equipped with blockingdevices; when the shift sleeve and the synchronizing ring rotate withrespect to each other, the blocking devices overlap each other partiallyand prevent axial motion of the shift sleeve beyond a predeterminedposition, as is generally known.

Additional advantages can be found in the description and theaccompanying drawings.

It is obvious that the characteristics already mentioned and those whichare to follow are applicable not only in the combinations stated, butalso in other combinations or also alone, without departing from thescope of this invention.

Examples of the invention are illustrated in the drawings and will beexplained in more detail in the following description.

FIG. 1 shows a highly schematic side view--partially in section--of partof a spur-geared, multi-range transmission as related to the invention.

FIG. 2 shows a radial view of part of a gear with the inclined surfacesas in the invention.

FIG. 3 shows a radial view of part of a synchronizing ring as works inthe invention with the gear of FIG. 2.

FIG. 4 shows the gear of FIG. 2 and the synchronizing ring of FIG. 3 inthe synchronized position.

FIG. 5 is an illustration similar to FIG. 4, however, in theunsynchronized position.

FIG. 6 is a schematic sketch to explain the resulting forces affectingthe inclined surfaces.

FIG. 7 is an additional schematic sketch to explain the resultingfriction moments.

FIG. 8 shows part of a cross-sectional representation for explanation ofthe blocking devices of synchronizing rings as in the invention.

In FIG. 1, (10) in a spur-toothed, synchromesh, multi-range,motorvehicle transmission. On the first shaft (11), a first gear (12) islocated; it cannot move axially and rotates with the shaft; the externaltoothing (13) of the gear (12) engages the internal toothing (14) of ashift sleeve (15) which can be moved axially as indicated by the arrow(6).

A synchronizing ring (20) is located axially next to the first gear(12); the ring (20) rotates with the first gear (12) and can be rotatedby a certain angle of rotation with respect to the gear (12). Thesynchronizing ring (20) has a conical friction surface (21) on the sidefacing away from gear (12).

The shift sleeve (15) and the synchronizing ring (20) have blockingdevices (22 and 23) respectively; these have the form of a type oftoothing and prevent axial movement of the shift sleeve (15) beyond theright face of the synchronizing ring (20) in FIG. 1 when thesynchronizing ring (20) is rotated with respect to the first gear (12).When (20) and (12) are not rotated to one another, they are in aalignment and do not block axial travel of the shift sleeve (15).

As in later explained in detail, inclined surfaces are provided on thecircumference of the first gear (12) and on the synchronizing ring (20);these surfaces are inclined from a radial plane of shaft (11) and engageone another. They form the circumferential wedge system which is onlysuggested by (25) of FIG. 1. A second gear (30) can rotate freely but isaxially located on the first shaft (11), to the right of thesynchronizing ring (20) of FIG. 1; (30) has an opposing surface (31),which also has a conical shape which runs parallel to the frictionsurface (21). There is an axial clearance between the opposing surface(31) and the friction surface (21), however this clearance is shownexaggerated in FIG. 1 for the sake of clarity.

The second gear (30) has external toothing (32) which meshes withexternal toothing (33) of a third gear (34) which is located axially onand rotates with a second shaft (35) which is parallel to the firstshaft (11).

When the range is to be changed with the driving moment to betransmitted from the first shaft (11) through the ratio of gears (30/34)to the second shaft (35), the following occurs:

In the operation position shown in FIG. 1, the first driven gear (12)rotates with the first shaft (11); the shift sleeve (15) andsynchronizing ring (20) rotate with it. Because of the clearance betweenthe friction surfaces (21/31), the first shaft (11) is not loaded.

To effect a range change, the shift sleeve (15) is moved in thedirection of the arrow (16), taking the synchronizing ring (20) with itaxially. When the friction surface (21) of the synchronizing ring meetsthe opposing surface (31) of the second gear (30), the difference inspeed between gears (12) and (30) causes a friction moment. Thisfriction moment rotates the synchronizing ring (20) with respect to thefirst gear (12.) The blocking devices (22, 23) prevent the shift sleeve(15) from being moved further axially from this moment on so the onlytransmission of power between the first gear (12) and the second gear(30) takes place in the friction contact of the friction surfaces(21/31). As a result of this friction contact, the speed of the twogears (12, 30) become matched until, when the speed difference reacheszero, the friction moment also reaches zero and the blocking elements(22, 23) now align with one another and no longer prevent axial movementof the shift sleeve (15). The shift sleeve (15) can now be moved farenough to the right that its internal toothing (14) can engage theexternal toothing (32) of the second gear (30) in its left half. Gears(12) and (30) are now coupled and rotate together so that transmissionof torque from the first shaft (11) to the second shaft (35) now occursthrough gears (30/34).

In order to control the synchronizing procedure described aboveautomatically by engaging the friction surfaces (21/31), thecircumferential wedge system (25) is provided; FIGS. 2 through 7 arereferred to in the following to explain the system.

From the greatly enlarged radial side view in FIG. 2, one can see thatthe first gear (12) has one (or more) trapezoidal-shaped apertures onthe circumference, which are limited in the circumferential direction bythe first peripheral inclined surfaces (41 and 41'). The aperture (40)runs symmetrically to a centerline (42) which runs parallel to the firstshaft (11).

FIG. 3 shows the related part of the synchronizing ring (20) which has aprojection (50) complementing the aperture (40). The projection (50) hassecond peripheral inclined surfaces (51 and 51').

The first gear (12) and the synchronizing ring (20) partially cover eachother axially when they are in the neutral or in a synchronizedoperating positions; for this reason, the outside diameter (52) of theexternal first contact surface of synchronizing ring (20) is slightlyreduced, while the first gear (12) has a corresponding inner secondcontact surface (53).

FIG. 4 shows the state mentioned above in neutral or synchronizedoperation; the projection (50) mates with the aperture (40), the relatedinclined surfaces (41/51) and (41'/51') contact one another. As seenfrom the circumference, there is symmetry with respect to the commoncenterline (42).

If now, however, the friction surface (21) reaches the opposing surface(31)-compare with FIG. 1-the resulting friction moment of thesynchronizing ring (20) will be rotated with respect to the first gear(12). FIG. 5 shows such an operating state; the rotation (viewed fromthe right in FIG. 5) occurs in such a manner that the synchronizing ring(20) rotates counterclockwise from the first gear (12). The firstinclined surface (41) of the first gear (12) now slides toward therelated second inclined surface (51) of synchronizing ring (20),which--when rotated relative to the gear by the circumferential portion(u)--leads to an axial displacement (z) of the synchronizing ring (20)with respect to the axially fixed first gear (12). In this case,centerlines (42a and 42b) are offset to one another on the circumferenceby the stated circumferential portion (u).

By comparing FIGS. 3 and 5, one can also recognize the function of theblocking elements (22 and 23). In the synchronized position (FIG. 3),blocking elements (22 and 23) can mesh, so they do not prevent axialmovement of the shift sleeve (15). In the non-synchronized, rotatedposition as in FIG. 5, the blocking elements (22 and 23) overlap eachother partially so that further movement of the shift sleeve (15) is notpossible beyond a pre-determined axial position. In this way,unsynchronized mis-shifting is prevented because the inner toothing (14)of the shift sleeve (15) cannot be made to mesh with the outer toothing(32) of the second gear (30).

FIGS. 6 and 7 illustrate the forces which occur at the wedge system(25).

In FIG. 6, one can recognize that the axial force (F_(a)) takes effectat the synchronizing ring (30); this is related to the radial force(F_(r) ') taking effect at the inclined surfaces (41/51) as follows:##EQU1## with α being the angle of the inclined surfaces (41 and 51)with respect to a radial plane in FIG. 6.

If one further considers that the forces (F) are applied to the conicalfriction surface (21) with a radius (r₁) and to the wedge system (25)with a radius (r₂)--each with reference to the axis of the first gear(12) and the synchronizing ring (30), the equation above can be writtenas follows: ##EQU2## with F_(r) being the radial force affecting thefriction surface (21). The axial force f_(a) induced by the wedge system(25) in turn induces a friction force ##EQU3## with β being the coneangle of the friction surface (21). The initial axial force (F_(a)) thusresults--by way of the friction surface (21) and the wedge system(25)--in a subsequent axial force (F_(A)) which follows the followingequation: ##EQU4##

By selecting a suitable friction coefficient (μ) for friction surface(21), the angles (α) and (β) as well as the radii (r₁) and (r₂), aconstant can be achieved which is greater than 1. In this case, aself-amplification--or coupling--of the friction moment occurs whichrises to a maximum value in a controlled manner until the first gear(12), the synchronizing ring (20) and the second gear (30) runsynchronously.

FIG. 8 shows a detail of another version in which synchronizing rings(20a 20b) are located on each side of the first gear (12'). To preventuncontrolled synchronizations from occurring if one of the synchronizingrings (20a or 20b) unintentionally comes into contact with the relatedgear, a mutual interlock is provided.

The interlock is a ball obstructor which comprises radial cavities (60a,60b) in the first gear (12'); balls (61a, 61b); apertures (62a, 62b) inthe synchronizing rings (20a, 20b); as well as a common radial cavity(64) in the shift sleeve (15').

As one can clearly see in FIG. 8, the diameter of the balls (61a, 61b)is larger than the radial thickness of the synchronizing rings (20a, 20bin the area of the apertures (62a, 62b). In the neutral positionillustrated in FIG. 8, upward travel of balls (61a, 61b) through aninner surface (63) is blocked by the shift sleeve (15') so the balls(61a, 61b) also partially engage in the radial cavities (60a, 60b) ofthe first gear (12') and thus block both synchronizing rings (20a, 20b)axially.

If now, for example, the shift sleeve (15') in FIG. 8 is moved to theleft, nothing is changed for the right ball (61a) because it is stillheld in the aperture (62a) by the inner surface (63) as well as by theradial cavity (60a). The left ball (61b), however, can move into theradial cavity (64) of the shift sleeve (15'), clearing the interlock ofthe shift sleeve (20b), allowing it to move to the left. This takesplace as follows: the shift sleeve (15') moves up to the resilient ring(66b) which is in a groove (65b) of the synchronizing ring (20b). Thesynchronizing ring (20b) is now moved to the left; its friction surface(21b) meets the related opposing surface (31b), at which point thesynchronizing procedure described in detail above takes place. Whenleaving this transmission range, a lateral limiting flank of the cavity(64) takes the ball (61b) with it and, thus, also the synchronizing ring(20b) until the ball (61b) falls back into the radial cavity (60b),again releasing the synchronizing ring (20b).

It is obvious that numerous variations are possible within the scope ofthis invention, especially ones which relate to kinematic reversals ofthe mechanism mentioned above.

As one example, the synchronizing ring could rotate with the second gear(30) and the first gear (12) could be provided with an opposing frictionsurface. Allowing the wedge system to operate between the shift sleeveand the synchronizing ring instead of between the first gear and thesynchronizing ring is also conceivable. Additionally, it is possible todivide the functions of the synchronizing ring into an actuating elementand a friction element, whereby the actuating element rotates with onegear and is rotable and axially movable by the wedge system with respectto the gear, while the friction element is a "floating" synchronizingring located between two opposing surfaces, one each on the actuatingelement and on the opposing gear.

I claim:
 1. A multi-range transmission, for motor vehicles, with a firstgear and a second gear located next to one another on a first shaft andsynchronizing means located between the first and second gears andmovable axially with respect thereto for synchronizing the speed for thetwo gears, whereby a synchronizing ring of the synchronizing means,which rotates with the first gear, is rotatable only a limited portionwith respect to the first gear and has a circumferential frictionsurface which, when actuating element is moved axially, can be broughtwith an opposing friction surface of the second gear, the synchronizingring has an inclined surface, inclined with respect to a radial planewhich contacts an inclined surface of the first gear so that whenfrictional engagement between the two friction surfaces occurs and axialforce directed toward the opposing friction surface is applied to thesynchronizing ring, the first gear rotates with and the second gearrotates on the first shaft, the second gear engages a third gear whichrotates with a second shaft aligned parallel to the first shaft, and ashift sleeve is movable over the first and second gears to lock the twogears together, wherein a synchronizing ring is provided on each side ofthe first gear, and blocking means is provided to prevent axial movementof one of the synchronizing rings when the other synchronizing ring ismoved.
 2. A multi-range transmission as in claim 1, wherein the blockingmeans comprises obstructor balls, at least one ball is partially locatedin an aperture of each synchronizing ring, the diameter of the ball islarger than the radial thickness of the synchronizing ring in the areaof the aperture whereby the ball can engage one of a radial cavity ofthe first gear and a radial cavity of the shift sleeve.
 3. A multi-rangetransmission as in claim 1, wherein each synchronizing ring is providedwith a resilient ring which the shift sleeve contacts in order to bringthe friction surface of that synchronizing ring into contact with itsadjacent opposing friction surface.
 4. A multi-range transmission as inclaim 1, wherein the shift sleeve and the synchronizing ring are eachprovided with blocking elements which at least partially overlap oneanother and only allow axial movement of the shift sleeve beyond apredetermined position when the blocking elements are in meshingengagement.
 5. A multi-range transmission, for motor vehicles, with afirst gear and a second gear located next to one another on a firstshaft and synchronizing means located between the first and second gearsand movable axially with respect thereto for synchronizing the speed ofthe two gears, whereby a synchronizing ring of the synchronizing means,which rotates with the first gear, is rotatable only a limited portionwith respect to the first gear and has a circumferential frictionsurface which, when actuating element is moved axially, can be broughtinto contact with an opposing friction surface of the second gear, thesynchronizing ring has an inclined surface, inclined with respect to aradial plane, which contacts an inclined surface of the shift sleeve sothat when frictional engagement between the two friction surfaces occursan axial force directed toward the opposing friction surface is appliedto the synchronizing ring, the first gear rotates with and the secondgear rotates on the first shaft, the second gear engages a third gearwhich rotates with a second shaft aligned parallel to the first shaft,and a shift sleeve is movable over the first and second gears to lockthe two gears together, wherein a synchronizing ring is provided on eachside of the first gear, and blocking means is provided to prevent axialmovement of one of the synchronizing rings when the other synchronizingring is moved.